Designed under radically new principles of propulsion, the Excelsior had the potential for becoming the fastest starship in the entire Federation, as at that time, the Starfleet record for faster-than-light travel was warp factor 14.1, set by the USS Enterprise in 2269. (TOS: "That Which Survives")

The Excelsior's bridge, manned by the ship's commanding officer, Captain Styles, and other officers

The Excelsior was days away from her first full field test of the transwarp drive, when she was unexpectedly called for duty. The crew of the USS Enterprise, attempting to rejoin CaptainSpock's katra with his regenerated body, hijacked the Enterprise for an illegal journey to the Genesis Planet.

The Excelsior sputters out, dead in space

Captain Styles, confident in his new "incredible machine," was ordered to pursue as the Enterprise entered warp, fleeing the system. However, Captain Montgomery Scott, assigned as captain of engineering aboard the Excelsior, had sabotaged the ship's transwarp computer, leaving the Excelsior dead in space. Proud of his accomplishment, Scott explained that "the more they over-think the plumbing, the easier it is to stop up the drain." (Star Trek III: The Search for Spock)

Following this embarrassing failure, the Excelsior essentially spent the next two years in spacedock. In 2286 she was briefly ordered to be launched during an apparent attack by an alien probe, but the Excelsior, as well as the spacedock, lost all internal power and was left stranded in her bay. (Star Trek IV: The Voyage Home)

Although never directly addressed, the only evidence that the Excelsior was a failure as a transwarp prototype can be found in the Star Trek: The Next Generation Technical Manual, which stated that "the attempt to surpass the primary warp field efficiency barrier with the Transwarp Development Project in the early 2280s proved unsuccessful...".

Sulu, who attempted to sneak the Excelsior into Klingon territory by traversing the Azure Nebula, was discovered by a Klingon battle cruiser commanded by Kang. While Sulu explained that the Excelsior was on a survey mission, studying the nebula, and had gotten lost due to a malfunction in the navigation system, Kang offered to escort the Excelsior back to Federation space. As the Excelsior emerged, she fired a modulated positron beam that triggered a thermochemical reaction, and successfully disabled Kang's ship.

The Excelsior then made a break for Qo'noS, but was almost immediately intercepted by three Klingon battle cruisers. The Excelsior and Klingon ships continued to exchange fire until the Excelsior was forced to retreat back to Federation space. (VOY: "Flashback")

The USS Excelsior was first mentioned in the script of Star Trek II: The Wrath of Khan. Kirk states that Sulu was going to have the command of the Excelsior by the end of the month. [1] Apparently, his presence aboard the Enterprise at that time was solely as a courtesy to Kirk.

The USS Excelsior was designed for the production of Star Trek III, after the review of several prototype studio model ideas. Built by ILM, this highly detailed studio model was reused for many guest appearances until 1994 when it was refurbished to become the USS Enterprise-B and later the USS Lakota. After that, a half-scale recreation was built for "Flashback," with minor differences – even though it was supposedly the same ship as seen earlier. For example, "Flashback" features the only appearances of the ship's warp nacelles glowing, although the episode also incorporated footage from Star Trek VI in which the nacelle sides did not glow.

In the German dubbing of Star Trek III Uhura's line "Would you look at that!" was changed to (re-translated) "Look at that: Thorndyke's idea!" This could provide insight into who was material to the creation of the ship. Done for lip-syncing purposes, common practice when dubbing episodes and movies, the name Thorndyke was introduced solely for this purpose and does not refer to any canonical figure in the Star Trek universe.

It is further explained that the arrogant Captain Styles was placed in temporary command by Fleet Admiral Morrow as part of an effort to sequester those with direct knowledge of Genesis and Starfleet's unwillingness to delay trial runs until the controversy subsided, due to the considerable investment in the ship's development.